洱海富营养化时间演变特征(1988-2013年)及社会经济驱动分析

Long-term trend of eutrophication state of Lake Erhai in 1988-2013 and analyses of its socio-economic drivers

基于1988-2013年的洱海流域社会经济统计数据与湖内水质历史监测数据,分析了社会经济指标和富营养化指标的逐年变化趋势,并借助Change-point Analyzer对指标进行了拐点分析.结果显示:过去25年洱海水体呈明显富营养化趋势,主要富营养化指标均出现过1次恶化拐点,总磷出现时间最早(1996年),其次是高锰酸盐指数(1999年),总氮、叶绿素a、透明度和综合营养状态指数则集中在2002-2003年期间出现拐点,叶绿素a浓度上升10余倍,透明度相应下降了近50%.流域主要社会经济指标出现了2~3次增长拐点,首次拐点集中出现在1994-1999年期间,明显早于富营养化指标恶化拐点出现时间.多元回归分析显示洱海总磷浓度受流域农作物种植业发展影响最大,其他水质指标则主要受流域畜牧业的影响.

This paper studies the long-term trend of socio-economic indicators with the watershed and water quality data of the lake from the year 1988 to 2013 AD at Lake Erhai,the second largest freshwater lake located in the Yunnan-Guizhou Plateau in southwestern China. A powerful analyzing tool called Change-point Analyzer is employed to analyze the inflection points of all-time series. Our results show that each of the main eutrophic indicator has a worsening inflection point over the past 25 years. The inflection point of total phosphorus( TP) appeared the earliest( 1996),followed by that of permanganate index( CODMn)( 1999).While,inflection points of total nitrogen( TN),chlorophyll-a( Chl. a),translucency( SD),and comprehensive trophic level index( TLIc) were in 2002-2003 with TN concentrations doubled,Chl. a concentrations increased 10 times and SD decreased by 50%.Lake Erhai ecosystem experienced an abrupt regime shift from a grass-type lake to an algae-type lake in 2002-2003. Most socioeconomic indicators for Lake Erhai Basin have two or three inflection points with the first one between 1994 and 1999,which is 2 to 3 years earlier than the inflection points of eutrophication index. This suggests uncontrolled rapid socio-economic development had directly promoted the eutrophication in Lake Erhai. The second one occurred from 2006 to 2010 when eutrophication indicators did not show a further deterioration trend,which may be related to effective pollution reduction measures of the basin and self-regulation capacity of lake ecosystem. Multiple regression analyses show that the development of animal husbandry and economic crop cultivation had the major impact on water quality. Therefore,our results suggest that increasing agricultural non-point source pollution control will be the key method to curb eutrophication in Lake Erhai.